As shown in FIG. 1, a switching node generally comprises peripheral units LTG (line/trunk groups), a computer platform CP, a message buffer MB and additional central units such as a switching network SN, protocol termination units CCNC (i.e. for the signalling system no. 7), background memory MD and control equipment NC.
The peripheral units perform key switching tasks related to the voice channels on the peripheral units. They therefore contain switching, operating and administrative programs and programs relating to information for the unit, such as equipment number, signalling, authorisations, directory numbers, individual characteristics for trunk lines and subscriber connections as well as information on the installed capacity and configuration of the relevant peripheral units. The central computer platform provides coordinated control for setting up and clearing down connections and reacts to administrative and error-related configuration changes.
The peripheral units are linked via the message buffer to one another and to the computer platform. The other central system components provide special functions for the switching system such as through connecting voice channels, processing signalling protocols, providing the operator interface or buffering mass data.
For reliability, the central components in a switching system are of redundant design (i.e. duplicated). In general, the peripheral units are not of redundant design. In the event of strict reliability requirements (such as retaining stable connections in the event of failure of a peripheral unit) they may be of redundant design.
If signalling and voice are disassociated and routed on separate paths and if the peripheral units are only tasked with processing signalling and/or converting without physically terminating the voice channels, then there are no restrictions on the number of terminable voice channels. These logical peripheral units are designed for this application in terms of capacity, processor performance, buffer size and message interface capacity.
Since more than one direction must be available to through connect voice between an A-side subscriber or an A-side trunk (i.e. a connection to a remote exchange) and a B-subscriber or a B-side trunk, then generally two separate peripheral units PE are involved in setting up and clearing down connection, as shown in FIG. 2. The classic peripheral unit only terminates the trunks for which it is responsible for processing the switching. Usually there are peripheral facilities to terminate n PCM30 (pulse code modulation) routes (e.g. n=4 for 120 trunks).
In this application, in which the voice is routed outside the exchange, there are no restrictions on the maximum number of terminable trunks that can be physically determined. In this instance, a peripheral device can process more than 120 trunks simultaneously for example. A network scenario in which the exchanges are used for connections routed outside the exchange is shown in FIG. 3.
The exchange responsible for controlling the connections routed outside the exchange can provide the A and/or B-side subscribers of classic TDM networks (classic telephone network with time division multiplexing) with known subscriber or network features. This includes in particular messages and dialogues that are required in certain situations (e.g. “you have dialed an incorrect number, please try again”, “the number has changed, please re-dial using 722-25940 or the query for authorisation to dial into a packet network).
In the classic case, in which the subscriber channel of the connection is routed into the exchange, these messages and dialogues can be provided by peripheral facilities equipped with the appropriate functions. If the subscriber data is however routed outside the exchange in a packet network, then an external system is often used (IVR, interactive voice response system). Alternatively, an existing TDM-based message system can also be used for packet network connections.
According to the prior art, known IVR systems are usually TDM-based (time division multiplex) and combine the entire range of functions to be universally useable. The disadvantage of this universality is however the costs incurred by the most effective use of an IVR system. In TDM-based data communications networks (e.g. the classic telephone network) with conventional exchanges, two usage scenario are used that are described below:
Firstly, peripheral units of the exchange are equipped with hardware modules to provide messages, DTMF (discrete tone multi-frequency) and/or voice recognition in the exchange. To play back a message or a dialogue, the subscriber/trunk is switched via a 64 kbit/s connection to a physical port of this special peripheral device for messages and dialogues.
From a switching point of view, this involves through connecting a trunk routed from an A-side peripheral device via the switching network to the B-side peripheral device with message and/or dialogue functionality. The B-side message/dialogue port acts like a B-side trunk. The type of message or dialogue functions to be played is determined by exchange-internal signalling to the peripheral device with message and/or dialogue functions or is pre-defined.
The advantage of this implementation lies in the integration of the message and/dialogue functions in the exchange that is very cost-effective. Furthermore, there is broader access to the hardware functions of the peripheral facilities for message and/or dialogue functions.
The disadvantage of this implementation is if the subscriber channel is packet based or is routed outside the exchange, this function can either not be used or can only be used with a downstream media gateway that bridges the network gateway between the TDM-based data communications network (classic telephone network) and the packet network (e.g. internet).
Furthermore, the voice data, which according to the prior art is available in PCM/TDM technology (pulse code modulation/time division multiplex), has to be converted to packet data. Furthermore, there is a subscriber data load for messages and dialogues to the controlling exchange and there is a loss of voice quality because of the conversion of subscriber data from TDM/PCM systems into packet data.
Secondly, messages and dialogues are also prepared at the network gateway between the packet and the TDM network or through a packet-based IVR system especially designed for message and/or dialog function. The message and/or dialogue functions are controlled through a call control server in the exchange that controls the connection. The advantage of this system is that packet-switching data communications networks (packet networks) can be used without the need for any TDM equipment since there is no additional conversion of the subscriber data from a TDM system to packet data.
The disadvantage of this system however is that the exchange that controls the exchange for connections routed to the packet network, has no access to the existing IVR functions in the packet network.